1. Field of the Invention
This invention relates to micrometer heads each mounted to a measuring instrument and a precision instrument for being utilized in measuring, precise feeding, positioning and the like, and more particularly to improvements in a zero adjusting mechanism (a reference position adjusting mechanism) of a micrometer head.
2. Description of the Prior Art
In general, the conventional micrometer heads are of a so-called screw-feed type, in each of which a spindle threadably coupled to a sleeve is transferred in the axial direction thereof due to rotation of a thimble. With the micrometer head of the type described, it is very convenient to be able to conduct the graduation matching at the reference position, i.e., zero adjustment when the micrometer head is mounted to a measuring instrument or the like.
The zero adjusting mechanism of the micrometer head is divided into two types. The first type is constructed such that the micrometer head is mounted to the measuring instrument or the like, the spindle is transferred to the reference position, and thereafter, the graduation is forcedly matched with the end edge of the thimble, that is, the zero adjustment is conducted. The other type is of such an arrangement that the graduation is previously matched with the end edge of the thimble, that is, the zero adjustment is conducted, and thereafter, the spindle is transferred to the reference position with the graduation position being left as it is. The latter is preferable from the above-described two types for matching of the graduation.
As the micrometer heads belonging to the latter type, i.e., the one in which the graduation matching is conducted, and thereafter, the spindle is transferred to the reference position with the graduation position being left as it is, there has heretofore been known one in which the conventional mechanism for transferring the spindle and the zero adjusting mechanism are provided separately of each other, and there is further provided a friction engaging means for suitably changing from one mechanism over to another (Japanese Utility Model Application Publication No. 22484/80), or the other, in which there is provided a change-over mechanism utilizing a link mechanism and the like, for example. However, the one adopting the friction engaging means is disadvantageous in that the operation is unstable and wear is high. The other adopting the change-over device is disadvantageous in that the working efficiency is very low, and the conventional operating section for transferring the spindle and the operating section for the zero adjustment are disposed close to each other, whereby it is combersome in use and the controllability is low. Furthermore, both constructions of the micrometer heads of the prior art are complicated in construction as a whole, require troublesome assembling work, are difficult to be manufactured at low costs, have a large number of parts and are low in controllability, so that the feed with high accuracy cannot be achieved satisfactorily.